Aquifer modelling of the Ganga-Mahawa sub-basin, a part of the Central Ganga Plain, Utter Pradesh, India

The Ganga-Mahawa sub-basin, which has an area of 1280 km(2) forms the weste rn part of the Central Ganga Plain in the Moradabad and Badaun districts of western Uttar Pradesh, India. The Bundelkhand granite forms the basement c omplex, overlain unconformably by the upper Vindhyan sequence, which is fur ther overlain by the Neogene (Middle and Upper) Siwaliks and finally by Qua ternary alluvium. Four geomorphological units, the Varanasi older alluvial plain, Aligarh older alluvial plain, terrace zones and the Ganga recent flo odplain, abandoned channels, channel scars and meander scars represent vari ous landforms. The hydrogeological cross-sections indicate the occurrence o f a single aquifer down to 120 m. Some influent seepage from the River Gang a could be seen around Gangeswari, but the rest of the River Ganga is efflu ent. Groundwater-flow modelling was carried out to assess the degree of Ganga ri ver and aquifer interaction. The River Ganga marks the western boundary; bo undaries to the northeast and southeast are set as fixed heads to simulate lateral inflow into and outflow from the sub-basin respectively. The easter n boundary is simulated as a no-flow condition. The Mahawa and Badmar river s are considered to be effluent. The area modelled is covered by a grid of 34 rows x 46 columns with three layers, viz., an unconfined aquifer, an aqu itard which is underlain by a semi-confined to confined aquifer. The permea bility distribution was inferred from morphometric analysis and pumping tes ts. Natural recharge due to monsoon rainfall forms the main input. The Rive r Ganga stage data at Ahar, Naora and Ramghat has been used for assigning s urface water levels and river bed elevations in the model. Abstraction from all existing deep and shallow tube wells has been assigned as output at va rious cells. A steady state flow simulation was carried out and calibrated against the June 1986 water level; subsequent transient conditions were cal ibrated up to May 1995. The computed groundwater balance was comparable to that estimated from field investigations. The aquifer modelling study has a ttempted to integrate all available information and provided a tool that co uld be used for predictive simulation. Copyright (C) 2000 John Wiley & Sons , Ltd.